2003 mustang, new system?

Ok to give some backround.

Car: 2003 Mustang

I am currently designing a new system. I have a RF HE2 12 DVC in a 1.5 sealed enclosure getting about 150watts RMS. Anyone familiar with a Mustangs trunk knows that they are not that big. I am considering fiberglassing the spare tire well into a sub box. I was originally thinking of just transfering the 12 into the new box, then I started thinking about looks and thought about going with 2 10's probably ID IDQ 10's. The more I thought about it I figured why not just get a nice set of DVC 8's.

So what would the pair of 8's sound like compared to single 12, I am not really into SPL more of an SQ person myself. I do listen to hip hop and R&B so I do want something that will sound good with that, then I also listen to rock, alternative, and country so I want something with tight bass for that.

The current 12 is running on 2 channels bridged off of an older Sony 475 so I figure with the 3ohm load the DVC is pulling I am probably getting 150watts RMS to it.

I plan on pushing the 8's with an older PPI A404.2 Art Series which should push 2x200@ 4ohms bridged, however I have heard that these amps were seriously under rated so it very well could be more than 200x2 to the 8's

So any suggestions for a nice 8, and how would they compare to my current DVC 12.

Thanks for your input, that was sort of the way I was leaning.

To pose another question I am trying to use as little space in the car as possible. I am toying with fiberglassing the spare tire well and putting one nice DVC 10 in it. Then yesterday while looking in the car for ideas I came to this thought. I have a rear seat delete in place. When you take the rear seat out of a Mustang you are left with 2 tubs, one on each side of the driveshaft hump. Considering there is no back seat I have these two tubs that are about 15"x21" and I can build it as deep as 10" or so which theoreticly would give me about 1.8cuft. Given that it is not a perfect cube(has slanted walls) even if I lost 40% of my figure I would still have over 1 cuft per side.

What would they sound like if I mounted them in the car rather than in the trunk? For example with the windows down would I loose any db's or would it sound just the same as if I put it in the trunk?

I am also toying with a box like this so that it can have some show appeal

It would be mounted so that the tops of the exposed magnets would be flush with the floor so I can build a cover of some sort to stealth it out. Would a box like that work if it had the right airspace even if the distance from the subs mounting surface to the bottom of the box would only be 3" or so?